Commercial gas turbines are known in the art for generating power. A typical gas turbine used to generate electrical power includes an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Ambient air may be supplied to the compressor, and rotating blades and stationary vanes in the compressor progressively impart kinetic energy to the working fluid (air) to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through one or more nozzles where it mixes with fuel and is injected into a combustion chamber where the fuel mixture ignites to generate combustion gases having a high temperature and pressure. The combustion gases then flow to the turbine where expansion of the combustion gases produces work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity.
Various design and operating parameters influence the production of nitrous oxides, carbon monoxide, unburned hydrocarbons, and other undesirable emissions in the combustion gases that exit the turbine. For example, the combustion gas temperature directly influences the production of the various undesirable emissions. Specifically, a higher combustion gas temperature associated with higher power operation generally increases the disassociation rate of diatomic nitrogen, increasing the production of nitrogen oxides (NOx). Conversely, a lower combustion gas temperature associated with reduced fuel flow and/or part load operation (turndown) generally reduces the chemical reaction rates of the combustion gases, increasing the production of carbon monoxide and unburned hydrocarbons. As another example, the residence time of the fuel mixture or combustion gases in the combustion chamber directly influences the production of the various undesirable emissions. Specifically, a longer residence time generally increases the NOx levels, while a shorter residence time generally increases the carbon monoxide and unburned hydrocarbon levels. Therefore, continued improvements in the combustor designs and methods for supplying fuel to the combustor would be useful to reducing undesirable emissions over a wide range of combustor operating levels.